WO2018196915A1

WO2018196915A1 - Roller screw drive

Info

Publication number: WO2018196915A1
Application number: PCT/DE2018/100316
Authority: WO
Inventors: Mario Kreutzer; Harry Schmeiko; Christian GAUBE
Original assignee: Schaeffler Technologies AG & Co. KG
Priority date: 2017-04-28
Filing date: 2018-04-09
Publication date: 2018-11-01
Also published as: DE102017109143A1

Abstract

The invention relates to a roller screw drive comprising two screw drive components (2, 3), namely a lead screw (2) and a lead-screw nut (3), and rollers (4), which roll between the screw drive components (2, 3) under the influence of a force acting between the screw drive components in an axial main load direction and which are guided in a cage assembly (5), wherein at least a part of the cage assembly (5) is designed as a load-bearing element which is active in the case of axial loading between the screw drive components (2, 3) against the main load direction.

Description

Roller screw

The invention relates to a roller screw drive suitable for use in a linear actuator according to the preamble of claim 1.

Such a roller screw is known for example from DE 103 54 064 A1. By a threaded spindle and a spindle nut of the roller screw thread grooves are formed in which rollers roll as rolling elements. The rollers of the known roller screw are guided in a cage, which has two straps arranged at a distance from one another, which span a plane to which the axis of rotation of the rollers is arranged in parallel. The axes of rotation of the rollers are aligned transversely to the two straps. Further roller screw drives are known, for example, from the documents DE 101 09 505 B4 and GB 2 361 286 A. In both cases, these are screw drives with rolling element feedback.

The use of a roller screw in an electromechanically actuated disc brake is known for example from DE 195 1 1 287 B4. The roller screw acts as a reduction gear, wherein a rotor of an electric motor radially surrounds the roller screw.

A roller screw with rollers, which are individually guided by cage segments, is disclosed for example in DE 101 13 510 B4.

WO 2009/053359 A1 describes a combined vehicle brake with an electromechanically actuated parking brake. A screw drive used in this device is designed as a ball screw drive. A plurality of coil springs inserted in a thread load the rolling elements, that is balls, with a force in the circumferential direction of the ball screw. DE 10 2013 206 080 A1 discloses a ball screw with a arranged on a threaded spindle nut, that is, spindle nut, and wound around the longitudinal axis of the threaded ball channel, in which in addition to the balls at least one coil spring is added, which at a nem Molded part is supported, which is inserted into a recess of the threaded nut.

The invention has for its object to provide a multi-purpose roller screw, which is characterized by a particularly favorable ratio between claimed space and transferable forces.

This object is achieved by a roller screw with the features of claim 1. The roller screw has in known per se basic construction two screw drive components, namely a threaded spindle and a spindle nut on. The thread of the roller screw drive can be designed either as a single thread or as a multi-start thread. In any case, rolls roll as rolling elements between the two screw drive components. In addition to cylindrical rollers, needles are also to be understood as rollers. The arrangement of the rollers in the roller screw an axial main load direction is determined in which forces between the two screw drive components are transferable. The roles of the roller screw are guided by means of a cage assembly, which is not necessarily in one piece. According to the invention, at least part of the cage assembly is designed as a load-bearing element, which in this function is effective against the main load direction when the roller screw is loaded axially.

The invention is based on the consideration that in a Wälzgewindetrieb different load conditions, both in terms of the frequency of these states as well as the amounts and directions of forces, occur asymmetrically. This asymmetry is taken into account in the roller screw that in a first load direction, namely the main load direction, forces are transferred largely or practically completely on the roles of the screw, whereas in the opposite direction of loading of the mechanically much weaker resilient cage is used as the main force-transmitting element , In a preferred embodiment, the cage assembly comprises a sleeve-shaped metal part, in particular sheet metal part, which is also referred to as a cage in the strict sense and has recesses for the rollers. In this case, each roller is preferably guided in a separate recess of the metal part.

In a particularly simple design, a plain bearing component of the roller screw drive is formed directly by the sleeve-shaped metal part, which is at least effective when acting between the two screw drive components an axial force against the main load direction. In this embodiment, the cage assembly may consist exclusively of the metal part. The metal part is supported in its function as a plain bearing component on its inner side directly on the threaded spindle and on its outer side directly on the spindle nut. Optionally, the sleeve-shaped metal part, which acts as a sliding bearing component against the main load direction at least when the roller screw is loaded, is provided with a friction and / or wear-reducing coating. Such a coating may be, for example, a plastic, in particular PTFE (polytetrafluoroethylene), containing coating or a DLC coating (diamond like carbon). In a corresponding manner, additionally or alternatively, one of the screw drive components or each screw drive component, that is to say both the threaded spindle and the spindle nut, can be coated with wear and / or friction reducing material. According to a further developed design, the cage assembly comprises at least one separate sliding element, which contacts at least one load of the roller screw against the main loading direction at least one of the two screw drive components. The sliding element can be firmly connected either to one of the screw drive components or to the metal part of the cage arrangement. In principle, embodiments are also feasible, in which the sliding element is firmly connected to any of the said parts.

The sleeve-shaped metal part of the cage assembly is formed in various configurations of the roller screw by the force of a helical spring Spring loaded, which is inserted in the helically wound channel formed between the screw drive components. The coil spring is supported by the spindle nut or an element attached to the spindle nut. Optionally, a rolling element, namely a ball, is inserted between the helical spring and the sleeve-shaped metal part. This rolling element provides the coil spring with a larger engagement surface compared to the thin-walled, sleeve-shaped metal part, which efficiently counteracts the risk of mispositioning of the coil spring. Like the helical spring, the sliding element can engage in the thread of the roller screw drive. With its end facing away from the metal part of the cage assembly, the coil spring can be supported on the sliding element, which is firmly connected to the spindle nut. If the end of the helical spring facing the sleeve-shaped metal part is supported on the metal part with the interposition of a ball, the ball, with suitable dimensioning, can transmit forces against the main load direction in addition to the sliding element within the roller screw drive. Such a function of the ball is not given, if - as is the case in preferred designs - the diameter of the ball is significantly smaller than the diameter of the rollers of the screw drive.

The roller screw is preferably a screw without Wälzkörperrückführung. The roller screw drive is suitable, for example, for use in an electromechanical brake of a motor vehicle. Several embodiments of the invention will be explained in more detail with reference to a drawing. Herein show:

1 shows a first embodiment of a roller screw drive, Fig. 2 shows a second embodiment of a roller screw drive,

3 shows a detail "X" of the roller screw drive according to FIG. 2, 4 shows a comparison with the embodiment of Figure 2 modified design of a Rollgengewindetnebs,

5 shows a roller screw with ball as additional rolling elements,

FIG. 6 shows a detail "Y" of the roller thread web of FIG. 5, FIG.

Fig. 7 to 10 a further design of a Rollgengewindetnebs with various types

Rolling elements.

Corresponding or basically equivalent parts are indicated in all figures with the same reference numerals. Unless otherwise stated, the following explanations relate to all exemplary embodiments.

A generally designated by the reference numeral 1 roller screw drive comprises two screw drive components 2, 3 namely a threaded spindle 2 and a spindle nut 3, between which rollers 4 roll as rolling elements. A force acting between the screw drive components 2, 3 is denoted by F. The force F acts in the main load direction of the roller screw 1, as outlined inter alia in Figures 1 and 2. Here, in the arrangement of Figure 1, the threaded spindle 2 and in the arrangement of FIG. 2, the spindle nut 3 is loaded with the force F. If the roller screw 1 is adjusted in the opposite direction, it is called a return stroke.

The rollers 4 are guided in a cage assembly 5, which in all embodiments, a sleeve-shaped metal part 6 and at least one spring 7, namely coil spring comprises. The designed as a sheet metal sleeve metal part 6 is in this case supported on the spindle nut 3 via the at least one spring 7. The metal part 6 is also referred to as a cage in the strict sense. The rollers 4 are cylindrical rollers which roll on threaded tracks 8, 9, which are formed on the one hand by the threaded spindle 2 and on the other hand by the spindle nut 3.

The sleeve-shaped metal part 6 of the cage assembly 5 has pockets 10 for guiding the rollers 4. Through the sleeve-shaped metal part 6, a tilting of the rollers 4 within the roller screw 1 is prevented. The threaded spindle 2 can be used as a driving element of the roller screw drive 1, wherein a torque via a drive, not shown, in particular electric drive, in a spindle journal 1 1 of the threaded spindle 2 can be introduced. By the rotation of the threaded spindle 2, the spindle nut 3 is displaced linearly, being secured against rotation in a manner not shown.

In the embodiment according to FIG. 1, the cage arrangement 5 is constructed exclusively of the sleeve-shaped metal part 6 and two springs 7, of which only one can be seen in FIG. The pockets 10 are formed as individual pockets for guiding each of a single roller 4. A helically wound channel formed between the thread tracks 8, 9, in which all the rollers 4, separated from one another by the metal part 6, is designated by 12. In this channel 12 and the springs 7, that is coil springs, inserted.

The arranged in a helical row successively pockets 10 extend over only a portion of the length of the sleeve-shaped metal part 6. A continuation of this helix is given by two support webs 13, 14, which also each describe a helix. In this case, the supporting web 13 formed by the metal part 6 is directed radially inwards and the support web 14 likewise formed by this metal part 6 is directed radially outward. The support webs 13, 14 serve the purpose of transmitting forces between the screw drive components 2, 3 as soon as the roller screw drive 1 is loaded in total against the main loading direction. Here, the sleeve-shaped metal part 6 acts as a sliding bearing element, wherein the inner support web 13 is supported on the threaded spindle 2 and the outer support web 14 on the spindle nut 3. The sleeve-shaped metal part 6, which for contacting the screw drive components 2, 3 is provided, has a friction-reducing coating.

A sliding bearing function of the cage assembly 5 is also given in the design according to FIGS. 2 and 3. Instead of an outer support bar, a sliding element 15 is present in this case, which, comparable to the spring 7, is inserted into a section of the helical channel 12. Here, the sliding member 15 is loaded by the spring 7 with a force in the tangential direction of the screw drive components 2, 3. The row of rollers 4 in turn is supported in the tangential direction of the screw drive components 2, 3 on the sliding element 15. As is apparent from FIG. 2, the sleeve-shaped metal part 5 as a whole has contouring adapted to the shape of the thread tracks 8, 9 and of the channel 12.

As regards the inclusion of all rollers 4, of the sliding element 15, as well as of two springs 7 each designed as helical springs in the helical channel 12 of the roller screw drive 1, the design according to FIG. 4 is identical to the design according to FIG. The roller screw drive 1 according to Fig. 4 differs from the embodiment of FIG. 2, characterized in that the springs 7 are supported with the interposition of a respective ball 16 on the sleeve-shaped metal part 6. This assumes that the length of the rollers 4 is at least as large as their diameter, which is given in the embodiment of FIG. In addition to the sliding element 15, the balls 16 enable the transmission of forces within the roller screw drive 1 under load against the main loading direction.

In the case of FIGS. 5 and 6, two sliding elements 15, which are also attributable to the cage assembly 5 in this case, are fastened to the spindle nut 3 by means of screws 17. Instead of the screws 17 also pins or other fastening means could be used. Thanks to the two springs 7, the sleeve-shaped metal part 6, in which the rollers 4 are guided, is displaceable within the spindle nut 3 in the axial direction. A Wälzkörperrückführung is, as in all other embodiments, not provided. The design according to FIGS. 7 to 10 differs from the design according to FIGS. 5 and 6 in that the cage arrangement 5 comprises, in addition to the sliding elements 15, radially inwardly or outwardly directed support webs 13, 14 which pass directly through the plate made of sheet metal , sleeve-shaped metal part 6 are formed. Thus, the threaded spindle 2 is slidingly mounted several times relative to the spindle nut 3. The pockets 10 in the sleeve-shaped metal part 6 are designed such that even in operating states in which the threaded spindle 2 is almost completely unscrewed from the spindle nut 3, as shown in Fig. 10, the rollers 4 are held in the cage assembly 5. The holding of the rollers 4 through the sleeve-shaped metal part 6, that is, the cage in the strict sense, is in the assembly of the roller screw 1 of advantage. Furthermore, the fact is advantageous that the sleeve-shaped metal part 6 has different, formed as webs areas, which are arranged below and above the axes of rotation of the rollers 4, that is a smaller or smaller distance from the central axis of the roller screw 1 than the center axes of the Have roles 4, which allows a particularly dense arrangement of the rollers 4 within the cage assembly 5.

LIST OF REFERENCES

Rollgengewindetrieb

screw

spindle nut

role

cage assembly

sleeve-shaped metal part

feather

thread path

Pocket, recess

spindle pin

channel

supporting web

Slide

Bullet

screw

Force in the main load direction

Claims

claims

1 . Rollengewindetneb, with two screw drive components (2,3), namely a threaded spindle (2) and a spindle nut (3), and between the screw drive components (2,3) under the action of a force acting in a main axial load direction force, in a cage assembly ( 5) guided rollers (4), characterized in that at least part of the cage assembly (5) is designed as an axial load between the screw drive components (2,3) against the main load direction effective, laser-carrying element.

2. Roller screw drive according to claim 1, characterized in that the cage assembly (5) comprises a sleeve-shaped, a plurality of recesses (10) for the rollers (4) exhibiting metal part (6).

3. Roller screw drive according to claim 2, characterized in that the sleeve-shaped metal part (6) is designed as a sheet metal part.

4. Roller screw drive according to claim 2 or 3, characterized in that the metal part (6) against the main load direction on the inside thereof directly on the threaded spindle (2) and on the outside thereof directly against the spindle nut (3) is supported.

5. Roller screw drive according to claim 4, characterized in that at least one of the components sleeve-shaped metal part (6), threaded spindle (2) and spindle nut (3) wear and / or friction-reducing coated.

6. Roller screw drive according to claim 2 or 3, characterized in that the cage assembly (5) comprises at least one sliding element (15) which contacts at least one screw drive component (2,3) when loaded against the main loading direction.

7. Roller screw drive according to claim 6, characterized in that the

Sliding element (15) fixed to one of the screw drive components (2,3) is connected.

8. Roller screw drive according to claim 6, characterized in that the

Sliding element (15) is firmly connected to the sleeve-shaped metal part (6).

9. Roller screw drive according to one of claims 2 to 8, characterized in that the sleeve-shaped metal part (6) formed by a helical spring (7), which in a between the screw drive components (2,3) formed, helically wound channel (12). is inserted against the spindle nut (3), optionally with the interposition of a rolling element, namely a ball (16), is spring-loaded.

10. Roller screw drive according to one of claims 1 to 9, characterized in that it is designed as a screw without Wälzkörperrückführung.